Aspects of the tail flip, escape response of a thermosbaenacean, Tethysbaena argentarii, were examined with the aid of S-VHS video. The first part of the escape action involves a 180° shift in orientation, where head and tail change position within 2/50 to 4/50 sec. This shift is caused by two successive, tail flips: first a ventral movement, which brings the tail region close to the thorax; then a dorsal motion, which causes the thorax/head region to flip backwards because of greater water drag in the tail region (tail fan). The 180° change in orientation is sometimes followed by a number a forceful dorso-ventral tail flips that promote rapid swimming in the new direction. The type of escape reaction in Tethysbaena argentarii is different from the ‘jet’stream' type of escape reaction seen in various shrimp, euphausids, and mysids, but it bears some similarity to that seen in stomatopods and in various crayfish where a 180° shift in orientation is also seen.